using Plots
plotlyjs()
x = y = range(-5, 5, length=300)
f(x, y) = x^2+y^2
surface(x, y, f,colorbar=false, alpha=0.9 ,xlabel = "x", ylabel = "y", zlabel = "f(x,y)")
wireframe(x,y,f)
contour(x,y,f)
x = y = range(-5, 5, length=300)
f(x, y) = x^2-y^2
surface(x, y, f,colorbar=false, alpha=0.9 ,xlabel = "x", ylabel = "y", zlabel = "f(x,y)")
x = y = range(-5, 5, length=300)
f(x, y) = x*y
surface(x, y, f,colorbar=false, alpha=0.9 ,xlabel = "x", ylabel = "y", zlabel = "f(x,y)")
x = y = range(-5, 5, length=300)
f(x, y) = x^2+y^2
g(x,y)= 2(x-1)+2(y-1)+2
surface(x, y, f,colorbar=false, alpha=0.9 ,xlabel = "x", ylabel = "y", zlabel = "f(x,y)")
surface!(x, y, g,colorbar=false, alpha=0.9 ,xlabel = "x", ylabel = "y", zlabel = "f(x,y)")